DESCRIPTION: In Drosophila, a specialized germ plasm forms at the posterior pole of the oocyte during oogenesis, and is required for the subsequent determination of the germ cells. Genetic analysis has revealed ten genes necessary for germ cell determination. These genes also are needed for formation of the abdomen, because in the absence of functional gene product, the posterior morphogenetic signal (Nanos) does not localize at the posterior pole. This proposal is primarily concerned with oskar, which plays a central role in the posterior determination pathway. The activity of a variety of genes normally ensures that oskar RNA and protein localizes to the posterior pole; this is critical because oscar protein dictates subsequent steps in germ plasm assembly. The laboratory of the principal investigator has demonstrated not only that oskar normally acts as the dose limiting factor for pole plasm assembly, but that ectopic localization of oskar RNA at the anterior of the oocyte is sufficient to stimulate the formation of an additional, mirror image abdomen and the formation of functional pole cells (germ line precursors) at the anterior of the resulting embryo.